1. Field of the Invention
The present invention relates generally to methods and apparatus for exchanging heat with the body of a patient.
2. Description of the Related Art
It has been discovered that the medical outcome for a patient suffering from severe brain trauma or from ischemia caused by stroke or heart attack is improved if the patient is cooled below normal body temperature (37xc2x0 C.). Furthermore, it is also accepted that for such patients, it is important to prevent hyperthermia (fever) even if it is decided not to induce hypothermia. Moreover, in certain applications such as post-CABG surgery, it might be desirable to rewarm a hypothermic patient.
As recognized by the present invention, the above-mentioned advantages in regulating temperature can be realized by cooling or heating the patient""s entire body. Moreover, the present invention understands that since many patients already are intubated with central venous catheters for other clinically approved purposes anyway such as drug delivery and blood monitoring, providing a central venous catheter that can also cool or heat the blood requires no additional surgical procedures for those patients. However, single purpose heat exchange catheters such as are made by Innercool Therapies of San Diego, Calif. and Radiant Medical of Portola Valley, Calif. can also be less optimally used.
Regardless of the particular catheter used, it is clear that heat must be removed from or added to the coolant that flows through the catheter. As recognized herein, it is desirable that a heat exchange system for a heat exchange catheter consume minimal energy and space. Small size is desired because space is often at a premium in critical care units. Moreover, as also recognized herein, for patient comfort it is desirable that such a heat exchange system generate a minimum amount of noise. As still further understood by the present invention, it is desirable that the heat exchange system be easy to use by health care personnel, and provide for monitoring systems and convenient temperature control. U.S. Pat. No. 6,146,411, incorporated herein by reference, discloses one such heat exchange system. It is the object of the present invention to still further address one or more of the above-noted considerations.
A heat exchange system for an indwelling heat exchange catheter includes a heat exchange bath configured to receive a conduit that carries working fluid to and from the catheter. The bath is filled with a heating/coolant fluid that exchanges heat with the working fluid. The system further includes a heat exchanger through which the heating/coolant fluid flows. The heat exchanger includes a refrigerant and a variable speed DC compressor. Moreover, a heating/coolant fluid pump circulates the heating/coolant fluid between the heat exchanger and the heat exchange bath.
In a preferred embodiment, the system includes a heating/coolant fluid level detector that communicates with the heating/coolant fluid. Preferably, the system also includes a working fluid level detector that communicates with the working fluid. Also, the system includes a controller that receives patient temperature input and target temperature input. The controller controls the temperature of the heating/coolant fluid in response to the patient temperature input and the target temperature input.
Preferably, the controller selectively energizes the working fluid pump. Moreover, in a preferred embodiment, the system includes a lid on the bath. The lid is spaced above the top of the heating/cooling fluid. In a preferred embodiment, the system includes a display that shows a graph of temperature, e.g., patient temperature as a function of time. The display also presents qualitative comments on cooling and/or heating.
In another aspect of the present invention, a heat exchange system for an indwelling heat exchange catheter includes a working fluid circuit that is connected to the catheter to carry a working fluid to and from the catheter. A heating/cooling circuit is thermally coupled to the working fluid circuit and includes a heating/cooling fluid that exchanges heat with the working fluid. In this aspect, a refrigerating circuit is thermally coupled to the heating/cooling circuit. The refrigerating circuit includes a refrigerant that exchanges heat with the heating/cooling fluid.
In yet another aspect of the present invention, a display is connected to a controller for displaying temperature related to a patient having a cooling catheter intubated therein. The display includes means for providing a continuous graph of patient temperature as a function of time as the patient is heated or cooled via the cooling catheter.
In still another aspect of the present invention, a fluid level detector includes a hollow container that defines a longitudinal axis and a radial axis. The fluid level detector also includes a light emitter that emits a light beam along a first light axis angled from the axes of the container. In this aspect of the present invention, the direction of the light beam through the container is altered when the light beam is refracted by the fluid in the container. A light detector unit is distanced from the first light axis for receiving the light beam only when the light beam passes through fluid in the container and otherwise not receiving the light beam. The light detector unit outputs a detection signal when the light beam is detected. The detection signal is representative of fluid level in the container.
In yet still another aspect of the present invention, a method is provided for controlling a heat exchange apparatus that is connectable to an indwelling catheter for circulating saline thereto. The method includes determining a difference between a patient temperature and a target temperature. Based on the difference, one of two control modes are entered.
In another aspect of the present invention, a heat exchange system for an indwelling heat exchange catheter includes a working fluid circuit that is connected to the catheter to carry a working fluid to and from the catheter. Moreover, a heating/cooling circuit is thermally coupled to the working fluid circuit. The heating/cooling circuit includes a heating/cooling fluid that exchanges heat with the working fluid. A refrigerating circuit is thermally coupled to the heating/cooling circuit. The refrigerating circuit includes a refrigerant that exchanges heat with the heating/cooling fluid. In this aspect, the system also includes a controller for controlling the circulation of the working fluid, heating/cooling fluid and the refrigerant. The controller includes a program for determining the power required to heat or cool a patient in which the catheter is disposed.
The details of the present invention, both as to its construction and operation, can best be understood in reference to the accompanying drawings, in which like numerals refer to like parts, and which: